Bump mods/signs_lib from `bd20f9b` to `1327cb2`

Bumps mods/signs_lib from bd20f9b to 1327cb2.

Commits

• 1327cb2 make sure digger is valid before checking for creative
• c08eb34 allow writing # on signs
• 3ee06f9 protect against nil player on rightclick
• 02c19e8 don't try to run the glow code if the sign's being punched by a machine
• 8b6f5e2 fix typo
• 85dd92f update register_sign to add glow effect for all signs with allow_glow check.
• 16b9251 Add glow feature to signs, with three brightness levels
• b0fac5e remove the old blue/starry background
• 34689b5 bump minimum engine ver
• 8b6e41c Fix warnings regarding use_texture_alpha
• Additional commits viewable in compare view